The present invention relates to an electronic endoscope system that is adapted to observe a fluorescence image of autofluorescence emitted from a body cavity wall irradiated with excitation light, as well as a normal image of the body cavity wall illuminated with white light, on a display device such as a monitor.
An example of such an electronic endoscope system is disclosed in Japanese Unexamined Patent Publication No. HEI 9-066023. FIG. 11 of the present application shows a configuration of an electronic endoscope system that is disclosed in FIG. 1 of Japanese Unexamined Patent Publication No. HEI 9-066023. The system includes a first solid-state imaging device 2A that takes a fluorescence image, and a second solid-state imaging device 3A that takes an RGB color image (normal image) with illuminating light using a frame sequential method. In the system, both signals outputted from the first and second solid-state imaging devices are processed by a video circuit 26A for a fluorescence image and a video circuit 24A for a normal images, respectively. The signals are then synthesized by an image synthesis circuit 28A to be displayed on a monitor device 40A. According to the operation of a display image selector switch 29A, one of the two kinds of images or both is displayed on the monitor device 40A.
An additional example of an electronic endoscope system is disclosed in Japanese Unexamined Patent Publication No. P2003-33324A. FIG. 12 of the present application shows a block diagram of the system that is illustrated in FIG. 16 of Japanese Unexamined Patent Publication No. P2003-33324A. The system disclosed in Japanese Unexamined Patent Publication No. P2003-33324A includes (see FIG. 12) a first lamp 124 that emits illuminating light for normal observation and a second lamp 125 that emits excitation light, and either one of the two kinds of light is selectively introduced into a light guide 133 by changing the position of a movable mirror 128. Image signals captured by CCD 137 are stored in a first memory 141 and a second memory 142, and are then displayed on a Hi-Vision monitor 115 through a display location selector circuit 144. When a selector switch 135 for displaying two images (hereinafter, referred to as a two-image-display switch) is turned ON, a normal image and a fluorescence image are displayed on the Hi-Vision monitor 115, simultaneously. That is to say, when the two-image-display switch is turned ON, the mirror 128 is turned to a position indicated by a solid line, so that the excitation light is introduced to the light guide 133. At the same time, the first memory becomes write-protected, and a normal image, inputted thereto immediately before that, is outputted repeatedly to provide a still image. On the other hand, after the excitation light is irradiated for a predetermined time period, a shutter 132 is closed, and fluorescence image signals taken during the time period are stored in the second memory 142. Then, the second memory 142 becomes write-protected, and thereafter, the fluorescence image signals stored in the second memory are outputted repeatedly to be displayed as a still image. The mirror 28 is then turned back to a position shown by a dotted line, and the shutter is opened. Thereby, normal images, taken with the illuminating light emitted from the first lamp 124, are sequentially stored in the first memory 141, so that the normal image is displayed as a moving image.
However, the system, shown in FIG. 11, has to be provided with the two imaging devices for the normal image and fluorescence image at the distal end portion of the endoscope. Compared with the case of a single imaging device being used, employing two imaging devices of the same size as that of the single device in the above case causes a larger diameter of the distal end portion. On the other hand, employing the same diameter of the distal end portion as the above case causes a smaller size of each of the imaging devices, which results in a higher cost of the system due to a reduced pixel size of each of the imaging devices, or a lower resolution due to a reduced number of pixels.
On the contrary, by employing such a configuration as shown in FIG. 12, it is possible to take both of the normal image and fluorescence image with a single imaging device. However, both of the images are selectively obtained by changing the movable mirror 128. Therefore, for example, since it is impossible to display both of the images as moving images simultaneously, it is not allowed to compare and observe the moving images of both of the images.
It is noted that when displaying the moving images of both of the normal image and fluorescence image simultaneously with a single imaging device, it is necessary to repeat a cycle of predetermined periods of taking both of the normal image and fluorescence image. As a result, since amount of information of each of both of the image signals is reduced by half in comparison with the case of taking only one of both of the images, both of the images are displayed with reduced resolutions.